Method for data communication via a voice channel of a wireless communication network

ABSTRACT

A system and method for data communication over a cellular communications network that allows the transmission of digital data over a voice channel using a vocoder that operates in different modes depending upon characteristics of the inputted signal it receives. To prepare the digital data for transmission, one or more carrier signals are encoded with the digital data using one of a number of modulation schemes that utilize differential phase shift keying to give the modulated carrier signal certain periodicity and energy characteristics that allow it to be transmitted by the vocoder at full rate. The modulation schemes include DPSK using either a single or multiple frequency carriers, combined FSK-DPSK modulation, combined ASK-DPSK, as well as PSK with a phase tracker in the demodulator. These modulation schemes permit data communication via a CDMA, GSM, or other type of voice traffic channel at a low bit error rate.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. application Ser. No.11/163,579, filed Oct. 24, 2005, the complete contents of which arehereby incorporated by reference.

TECHNICAL FIELD

The present invention relates generally to data communication over atelecommunications network and, more particularly, to data communicationover a telecommunications voice channel such as a CDMA or GSM voicetraffic channel.

BACKGROUND OF THE INVENTION

Wired telephone systems were originally designed to carry speech toenable voice conversations over long distances. More recently, publicswitched telephone systems have become a primary medium for transmittingnot only voice, but also non-speech data, such as by use of facsimilemachines that transmit image information over the telephone lines, or bymodems that exchange digital data of various forms (text, binaryexecutable files, image or video files) over these same phone lines.

Today, cellular and other wireless communication systems are in muchgreater use for purposes of both voice and data communication. Mostcellular communication in use in the world today utilize either the GSM(including UMTS) or CDMA (IS-95 or CDMA2000) communication systems.These systems transmit voice data over a voice traffic channel using amodulated carrier wave. For example, 2G GSM uses GMSK modulation andIS-95 CDMA uses PSK modulation. Prior to modulating the voice data forwireless transmission, the voice input is run through a speechcompression circuit such as a vocoder to compress the voice input into asmaller amount of data. This reduces the amount of voice data that needsto be transmitted via the wireless network, thereby permitting the useof a smaller bit rate and a greater number of users sharing the samecommunication system.

Various vocoder techniques have been proposed and used. The most commonare various forms of linear predictive codings (LPC); for example, 2GGSM uses a RPE-LPC speech codec, while IS-95 CDMA uses a variable rateCELP codec. These predictive compression techniques are designedspecifically for voice encoding and, as such, are designed to filter outnoise and other non-speech components. As a result, the transmission ofdigital data (such as ASCII text, byte codes, binary files) can beproblematic since the vocoder processing can corrupt the digital data,making it unrecoverable at the receiving end of the transmission. Forexample, the recently introduced Qualcomm™ 4G Vocoder is a CDMA2000device that exhibits a time-varying, non-linear transfer function which,while acceptable for voice encoding, can impose significant distortionwhen attempting to transmit digital data via the vocoder.

The 4G vocoder uses the 3gpp2 standards-based EVRC-B codec having a fullrate of 9.6 kbps. The codec also supports lower bit rates, including a4.8 kbps half rate and a 1.2 kbps eighth rate. These lower rates areused when the vocoder determines that the full rate is not needed toadequately transmit the sound signals it receives. For example,background noise is typically transmitted at the one-eighth rate. TheEVRC-B vocoder uses these different rates to achieve a target rate thatcan be controlled by the wireless carrier and, as a result, this overallencoding process can make it difficult to successfully send non-speechdata through the vocoder.

SUMMARY OF THE INVENTION

The present invention provides a method of data communication using awireless communication network that allows the transmission of digitaldata over a voice channel of the communications network. In accordancewith one embodiment, the method includes the steps of:

-   -   (a) modulating one or more carrier signals with digital data        using differential phase shift keying modulation of the one or        more carrier signals, thereby producing a modulated carrier        signal;    -   (b) transmitting the modulated carrier signal across a voice        channel of a wireless telecommunications network;    -   (c) receiving the modulated carrier signal transmitted via the        wireless telecommunications network; and    -   (d) demodulating the received modulated carrier signal back into        the digital data.

Preferably, differential binary phase shift keying encoding is used,although quadrature and other DPSK encoding can be used depending uponthe resulting bit error rate for a particular application.

In accordance with another aspect of the invention, there is provided amethod of communicating digital data via a wireless telecommunicationsnetwork using a voice encoder that operates in different modes accordingto a classification of incoming data into categories. These categoriesinclude at least voiced, unvoiced, and transient speech, wherein each ofthe different modes is associated with a coding scheme for encoding theincoming data. The method comprising the steps of:

-   -   (a) inputting into the voice encoder a modulated carrier signal        having discontinuities and energy characteristics that cause the        voice encoder to classify the modulated carrier signal as        transient speech;    -   (b) obtaining an encoded output that is generated by the voice        encoder using the inputted modulated carrier signal;    -   (c) transmitting the encoded output across a voice channel of        the wireless telecommunications network;    -   (d) receiving the encoded output transmitted via the wireless        telecommunications network;    -   (e) generated a decoded modulated carrier signal by decoding the        received encoded output using a voice decoder; and    -   (f) demodulating the decoded modulated carrier signal.

In accordance with yet another aspect of the invention, there isprovided a method of wirelessly transmitting digital data using anEVRC-B vocoder. The method comprises the steps of:

-   -   (a) encoding digital data by modulating at least one carrier        signal with the digital data and producing therefrom a modulated        carrier signal having discontinuities and energy characteristics        that cause the vocoder to classify the modulated carrier signal        as transient speech;    -   (b) inputting the modulated carrier signal into an EVRC-B        vocoder;    -   (c) obtaining an encoded output from the vocoder; and    -   (d) transmitting the encoded output via an antenna.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred exemplary embodiments of the invention will hereinafter bedescribed in conjunction with the appended drawings, wherein likedesignations denote like elements, and wherein:

FIG. 1 is a block diagram depicting an electronic communication systemconstructed in accordance with the invention;

FIG. 2 is a pair of plots showing BPSK encoding of a CDMA data frame ata bit rate of 10 bits/frame;

FIG. 3 a plot of a BPSK baseband as in FIG. 2, but at a bit rate of 12bits/frame;

FIG. 4 depicts a sample vocoder output using the BPSK waveform of FIG.3;

FIG. 5 depicts a 500 Hz carrier modulated by BPSK using a random bitpattern at 10 bits/frame;

FIG. 6 is a sample vocoder output using the BPSK waveform of FIG. 5;

FIG. 7 is a block diagram of a BPSK demodulator;

FIG. 8 is a constellation plot of sample BPSK demodulated data;

FIG. 9 depicts an overview of the speech classification and ratedetermination scheme used by EVRC-B vocoders;

FIG. 10 is a 500 Hz carrier modulated by DBPSK using a random bitpattern at 10 bits/frame;

FIG. 11 depicts a constellation plot of the sample DBPSK demodulateddata of FIG. 10;

FIG. 12 depicts a constellation plot of sample DQPSK demodulated data;

FIG. 13 is a block diagram of a BPSK demodulator that uses a Costas loopfor phase tracking;

FIG. 14 is a flow chart of a multi-DPSK modulation scheme;

FIG. 15 depicts two DBPSK modulated carrier signals at differentfrequencies and the resulting composite modulated carrier signalobtained by using the process of FIG. 14;

FIG. 16 is a flow chart of a combined FSK-DBPSK modulation technique;and

FIG. 17 is a flow chart of a combined ASK-DBPSK modulation technique.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, there is shown an electronic communication system10 constructed in accordance with the invention. The communicationsystem 10 includes a conventional cellular communication network havinga voice traffic channel that is used for two-way transmission of voicedata between cellular telephones. The communication system 10 alsoincludes the ability to utilize the cellular system voice channel toexchange digital data containing information other than speech or otheraudio. As will be discussed in greater detail below, this datacommunication is carried out at least in part using differential phaseshift keying modulation of one or more audio frequency carrier wavesusing the digital data. This approach enables data communication via thesame voice channel that is used for speech transmission and, with properselection of carrier frequency and bit rate, permits this datatransmission to be accomplished at a bit error rate that is acceptablefor most applications.

The communication system 10 includes in general a cellular communicationnetwork 12 connected to a land telephony network 14 which together areused to provide voice and data communication between a passenger vehicle20 and a call center 40. Vehicle 20 has an onboard electronics system, aportion of which is shown at 22. Electronics system 22 has a telematicsunit 23 that includes the components normally found in a cellularcommunication device, such as a CDMA compatible chipset 24 and antenna26 that enables use of the cellular network 12 to permit a vehicleoccupant to carry on voice conversations using a speaker 28 andmicrophone 30. These components of telematics unit 23 can be implementedin a conventional manner, as will be known to those skilled in the art.Apart from the microphone 30 input, onboard system 22 also includes atleast one pushbutton 32 that can be used to initiate a voicecommunication with a live advisor 42 located at the call center 40.

In accordance with 4G CDMA systems, voice data from both the vehicleoccupant (not shown) and the live advisor 42 are encoded using a vocoderto compress the speech prior to wireless transmission over the voicetraffic channel via the cell tower 16. Once received over the wirelessnetwork, the encoded speech is then decoded by the vocoder for thelistener. The vocoder is incorporated into the chipset 24 as well as ina CDMA compatible module 18 located in the base equipment at the celltower 16. Although various compression codecs can be used, in theillustrated embodiment, the 4G vocoder is implemented as a time-varying,non-linear filter. Various such codecs are well known using linearpredictive techniques; for example, a RPE-LPC codec or a fixed orvariable rate CELP codec. Any suitable codec (whether linear predictiveor not) can be used in the system 10 of FIG. 1.

In addition to the typical voice data transmission over the voicetraffic channel, the communication system 10 enables data communicationvia this same voice traffic channel and through the vocoder 18, 24. Thisis accomplished using a modem on either side of the vocoder; that is,using a first modem 34 incorporated into the onboard vehiclecommunication system 22 and a second modem 44 located at the call center40. These modems can have the same construction and operation so thatonly modem 34 will be described, and it will be appreciated that thedescription of modem 34 applies equally to modem 44. As shown in FIG. 1,the telematics unit 23 can switch or multiplex the CDMA 4GV chipset 24between the modem 34 and the telephony devices 28-32 so that thecellular communication network 12 can be used for either voice or datacommunication, or both, even during the same call.

Regardless of whether the cellular call is initiated at the vehicle 20or call center 40, the transmitting modem can use a predefined tone(e.g., 2225 Hz) or series of tones to alert the receiving modem of therequested data transmission, and the various attributes of the dataconnection can then be negotiated by the two modems. To enable datacommunication over the voice channel, the modem applies a differentialphase shift keying (DPSK) encoding to convert the digital data beingtransmitted into DPSK data that can be successfully sent via the vocoder18, 24 and over the voice traffic channel of the cellular network 12. Inthe different illustrated embodiments, one or more particular forms ofDPSK encoding are used; for example, differential binary phase shiftkeying (DBPSK) modulation. As will be discussed farther below, encodingof the digital data is implemented by modem 34 using one or more carriersignals that are modulated with the data using a DPSK encoder/decoder36.

As illustrated in FIG. 1, modem 34 and its encoder/decoder 36 can beimplemented using software running on the telematics microprocessor 35.This software can be stored in the telematics memory 37. Otheralternative implementations will be apparent to those skilled in theart; for example, the modem 34 could be incorporated into the 4GVchipset 24, or can be implemented using a dedicated IC or other hardwarecomponent, or the modem software could be stored on processor 35 itselfor on other memory not shown.

On the vehicle 20, the digital data being DPSK encoded and sent viamodem 34 can be obtained by the telematics unit 23 from one or morevehicle system modules (VSMs) 38 over a vehicle network 39. Thesemodules 38 can be any vehicle system for which information transmissionis desired to or from the call center 40 or other remote device orcomputer system. For example, one VSM 38 can be a diagnostic system thatprovides diagnostic trouble codes or other diagnostic information to thecall center 40. As another example, VSM 38 can be a GPS-enablednavigation system that uploads coordinates or other such informationconcerning the vehicle's location to the call center. Data can betransmitted from the call center (or other remote device or computersystem) to the vehicle as well. For example, where VSM 38 is anavigation system, new maps or other directional or point of interestinformation can be downloaded to the vehicle. As another example, a VSM38 can be an infotainment system in which new music or videos can bedownloaded and stored for later playback. Furthermore, the term “digitaldata” as used herein includes not only information, but also executablecode such that new programming can be downloaded to the vehicle via thevoice traffic channel from a server or other computer. Those skilled inthe art will know of other such VSMs 38 and other types of digital datafor which communication to and/or from the vehicle 20 is desired.

The vehicle network 39 can be implemented as any suitable network, suchas a controller area network (CAN), a media oriented system transfer(MOST), a local interconnection network (LIN), an Ethernet, a local areanetwork (LAN), and can utilize appropriate connections and protocolssuch as those that conform with known ISO, SAE and IEEE standards andspecifications. A separate infotainment network (not shown) can also beincluded for access by the telematics unit 23 to a vehicle radio system,in which case the speaker 28 could be eliminated and instead the vehicleradio system speaker(s) used for audio output during voice conversationsthrough the communications system 12.

Land network 14 can be a conventional land-based telecommunicationsnetwork that is connected to one or more landline telephones andconnects wireless carrier network 12 to call center 40. For example,land network 14 can include a public switched telephone network (PSTN)and/or an Internet Protocol (IP) network, as is appreciated by thoseskilled in the art. Of course, one or more segments of land network 14could be implemented through the use of a standard wired network, afiber or other optical network, a cable network, power lines, otherwireless networks such as wireless local area networks (WLANs) ornetworks providing broadband wireless access (BWA), or any combinationthereof. Furthermore, call center 40 need not be connected via landnetwork 14, but could include wireless telephony equipment so that itcan communicate directly with wireless network 12.

Call center 40 includes not only the live advisor 42 and modem 44, butalso several other components. It includes a PBX switch 46 to routeincoming calls either to one or more telephones 48 for voicecommunication or to modem 44 for data transmission. The modem 44 itselfcan be connected to various devices such as a server 50 that providesinformation services and data storage, as well as a computer used by thelive advisor 42. These devices can either be connected to the modem 44via a network 52 or alternatively, can be connected to a specificcomputer on which the modem 44 is located. The various components ofFIG. 1 include some that are conventional and others that can beimplemented based upon the description contained herein and theknowledge possessed by one skilled in the art. For example, although themodems 34, 44 and their DPSK encoder/decoder are not conventionalcomponents, techniques for implementing DSPK encoding and decoding areknown and can be implemented by those skilled in the art using suchcomponents as DSPs and ASICs. Similarly, the other features needed toimplement the modems 34, 44 are all well known to those skilled in theart.

Turning now to FIGS. 2-8, various phase shift keying (PSK) approachesand results will be described. Because the vocoder used for cellularcommunication filters out frequencies above that needed for speechtransmission, successful data transmission over the cellular voicetraffic channel is limited to using frequencies at or below severalkilohertz. Thus, where data modulation techniques are to be used, thecarrier frequency should be limited to those within this upperfrequency. FIG. 2 includes two plots of a random bit pattern used forbinary phase shift keying (BPSK) modulation, the first plot (a) beingthe baseband BPSK representing the random 0011101011 bit pattern, andthe second plot (b) being of a 500 Hz carrier frequency modulated withthe bit pattern using BPSK. For a sampling rate of 160 samples at an 8kHz sampling frequency, these ten bits represent a typical 20 ms frameof data, such as is used in CDMA. For comparison, FIG. 3 is a similarBPSK baseband waveform, but at a bit rate of 12 bits/frame, with thewaveform depicting two and a half frames of data. This same FIG. 3waveform is shown in FIG. 4 after it has been sent through the vocoderwithout first being used to modulate an audio frequency carrier. Thefiltering carried out by the vocoder makes the digital dataunrecoverable from the (FIG. 4) output of the vocoder. Where BPSKmodulation of a 500 Hz carrier frequency is used (FIG. 5), the resultingoutput of the vocoder (FIG. 6) does retain to at least some extent theoriginal data.

Looking at FIG. 5 in greater detail, the modulated 500 Hz waveform ofFIG. 5 is at a bit rate of 10 bits/frame using the following random bitpattern:

-   -   0100001100001001101111001.

The resulting vocoder output of FIG. 6 can then be decoded by extractingthe phase information to resolve the waveform back into the originaldigital data. This can be done in a known manner such as is shown inFIG. 7 in which the vocoder waveform is multiplied by a sine waveformand the result summed to get I-axis data points, and is also separatelymultiplied by a cosine waveform to get Q-axis information. Digitalprocessing techniques for decomposing the vocoder waveform according toFIG. 7 and generating from it the resulting bit pattern is well known tothose skilled in the art. A sample constellation plot of sample bitpatterns run through the vocoder using BPSK is shown in FIG. 8. As thisconstellation diagram shows, the use of BPSK through the vocoder doesnot do well in retaining the original digital data and, as a result, hasa bit error rate (BER) that is unacceptably high for most applications.The loss of information using the BPSK appears to be the result of thenon-linear, time-varying attributes of the vocoder which can introducephase drifts in the signal passing through the vocoder.

Apart from the loss of information as a result of this apparent phasedrift, successful transmission of the digital data through the vocoderalso can be largely dependent on the encoding and transmission rate usedby the vocoder. For 4G vocoders such as Qualcomm's® which use an EVRC-Bcodec that follows the 3GPP2 C.S0014-B ver. 1.0 specification (availableat www.3gpp2.org), different rates are used for different types ofspeech, tones, and background noise. In general, the vocoder encodes andtransmits incoming data at a rate that is determined by classifying theinputted signal into categories representative of different types orportions of speech. These categories include voiced, unvoiced, andtransient, as well as silence and up- and down-transients. Dependinginitially upon this classification, but also upon additional tests, thevocoder selects a particular operating mode in which it uses aparticular coding scheme and rate to encode and transmit the receiveddata. Generally, this process is carried out on a frame by frame basis,with each frame corresponding to 20 ms of data sampled at 8 kHz. Forvoice communications, the process is designed to provide a faithfulreproduction of speech while accommodating other communication needs(such as ring-back tones) and attempting to minimize bandwidthutilization. However, this process can significantly inhibit datacommunications over the voice channel because it can result in less thanfull rate transmission. Without full rate transmission, it can bedifficult if not impossible to transmit the digital data through theEVRC-B vocoder at a bit error rate that is acceptable for mostapplications.

For prior generation vocoders that utilize EVRC-A, an incoming signalneed only look like speech to get full rate. Thus, modulation techniquessuch as continuous FSK could be utilized to obtain full rate. For the 4Gvocoders, however, the ability to achieve full rate is more difficult.FIG. 9 depicts an analysis of the EVRC-B speech classification schemecontained in the 3GPP2 C.S0014-B ver. 1.0 specification, showing thedifferent tests used to classify the incoming data and which of thosetests lead to full rate transmission. EVRC-B uses three main anchoroperating points (AOP's): AOP0, AOP1, and AOP2. These operating pointsare used in determining the rate selection and the anchor operatingpoints themselves are determined based on a target average rate that canbe adjusted by the wireless carrier. Thus, a service provider desiringto send digital data through the vocoder typically cannot control theanchor operating point determination. Instead, obtaining the desiredfull rate can be accomplished by modulating or otherwise conditioningthe encoded carrier signal according to one or more of the paths of FIG.9 that lead to the full rate determination.

In general, the process of FIG. 9 classifies the incoming data as one ofa number of categories of speech, such as transient or voiced, and basedon that categorization determines if it is to be transmitted at fullrate. As a part of the EVRC-B vocoder processing, a Levinson Durbinrecursion is applied and, regardless of the classification of the speechas transient or otherwise, the an error parameter of this recursion ismonitored to determine if full rate should be assigned. In particular, aStoporder30 iteration index is calculated and if this value is less thanor equal to four, then full rate transmission is used. This allows forring back tones to be transmitted at full rate. As indicated in FIG. 9,if the incoming data is classified as transient speech, then full rateis assigned. This will be true regardless of whether the vocoder isoperating in AOP0 mode (in which case the transient speech will beclassified as speech giving full rate), or instead operating in AOP1 orAOP2 mode.

To obtain a categorization of the incoming data as transient speech, ithas been found that, by conditioning the incoming data signal such thatit has discontinuities and appropriate energy characteristics, thesignal will be interpreted by the vocoder as transient speech andthereby assigned full rate. Thus, in view of the characteristics of thecoding scheme discussed above in connection with FIGS. 2-8 and the needto obtain full rate, successful transmission of data through the EVRC-Bvocoder can be achieved by selection of a modulation scheme that encodesthe digital data into one or more carrier signals in a manner that (1)survives the particular linear predictive coding scheme used (e.g.,CELP) and (2) imparts discontinuities and energy characteristics to thecarrier signal(s) such that the vocoder classifies the inputted signalas transient speech. These discontinuities and energy characteristicswill be discussed in greater detail below in connection with particularmodulation schemes, a number of which will now be discussed.

Turning to FIGS. 10 and 11, a first of several modulation techniquesusing differential phase shift keying (DPSK) will now be discussed. Theuse of DPSK avoids the phase problems introduced by the vocoder. TheDPSK modulates the carrier in accordance with the difference betweensuccessive information bits in the bit pattern and, in doing so,eliminates the problems caused by random phase drifts. Preferably,differential binary phase shift keying (DBPSK) is used, an example ofwhich is shown in FIGS. 10 and 11. In FIG. 10, the same bit pattern fromFIG. 5 is again used, but this time is used to modulate the 500 Hzcarrier using DBPSK. FIG. 11 shows the constellation diagram for thedecomposed vocoder output after it has been subjected to DBPSK decoding.As this plot shows, the results of demodulation are highlydifferentiated along the I-axis with the zeros and ones of the bitpattern centralized around two nodes on either side of the Q-axis lineextending through the origin. Thus, the original digital data can berecovered with a relatively low bit error rate. Sample data using DBPSKsuch as is shown in FIG. 10 was tested using a Qualcomm® 4G vocoderrunning in different operating modes. The bit error rate of the sampledata using a carrier frequency of 500 Hz and 500 bits/sec (10bits/frame) was about 1.5%. Other combinations of frequencies and bitrates (bits/frame) can be used as long the resulting bit error rate isacceptable for the particular application involved. For example, usingDBPSK at 500 bits/sec, good results have been obtained at carrierfrequencies of 500 Hz, 800 Hz, 850 Hz, 900 Hz, 950 Hz, 1000 Hz, 1300 Hz,1350 Hz, and 1850 Hz, and that these carrier frequencies can be variedup and down about 50 Hz without significant degradation of the bit errorrate. This gives preferred frequency ranges of 450-550 Hz, 750-1050 Hz,1250-1400 Hz, and 1800-1900 Hz. For two-way communication over the voicechannel, different frequencies are preferably used in each directionwith enough frequency separation between them; for example, 500 Hz and950 Hz.

As indicated in FIG. 10, the use of DPSK results in phase shifts thatprovide discontinuities in the modulated carrier signal which are one ofthe features identified above as being helpful in having the signalcategorized by the vocoder as transient speech. The benefit ofdiscontinuities in the modulated carrier signal inputted into thevocoder is that it gives the signal low periodicity which is one of thefactors used by EVRC-B vocoders in categorizing the incoming signal.Periodicity of the input signal is determined by the vocoder using acalculated normalized autocorrelation function (NACF) of the secondsubframe, which is referred to herein as NACF_(sf2) and can be computedusing the equation for it given in the 3GPP2 C.S0014-B ver. 1.0specification. Where NACF_(sf2) is below a threshold value associatedwith unvoiced speech, the periodicity of the signal is considered lowand this is one indicator used by the vocoder that the signal should beclassified as transient speech. The unvoiced threshold value, referredto as UNVOICEDTH, is determined by the vocoder based on a signal tonoise ratio. The phase shift discontinuities resulting from the DPSKmodulation achieve this low value for NACF_(sf2).

Another feature of the incoming signal analyzed by the vocoder indetermining speech classification (voiced, unvoiced, transient, etc.) isthe energy characteristics. Two of these are bER (band energy ratio) andvER2 which is a calculated value based on the ratio of the current frameenergy to a three frame average voice energy. bER is a measure of theratio of energy contained in a lower frequency band of 0-2 kHz to theenergy contained in a higher frequency band of 2-4 kHz. It is computedusing the equation:

${bER} = {\log_{2}\frac{EL}{EH}}$where EL is the amount of energy contained in the 0-2 kHz frequency bandand EH is the amount of energy contained in the 2-4 kHz frequency band.To meet the requirements for transient speech, most of the energy mustbe located in the lower frequency band such that bER>0. Equations andtechniques for determining EL and EH for each frame of the inputtedsignal are known to those skilled in the art.

For vER2, transient speech requires that the calculated value mustexceed a fixed threshold of −15, with vER2 being determined according tothe equation:

${{vER}\; 2} = {{MIN}\left( {20,{10*\log_{10}\frac{E}{vEav}}} \right)}$where E is the energy of the current frame, and vEav is the averageenergy over three previous voiced frames. Although a goal of themodulation techniques disclosed herein is to avoid any frames beingcategorized as voiced by the vocoder, a typical telephony connectionover the cellular communication system 12 will involve not just datatransmission, but actual speech as well (e.g., between the vehicleoccupant and call center personnel 42) so that there will typically bevoiced frames in which the vEav can be determined and, even if not, thevocoder uses a default value of 0.1 for vEav where there are framesclassified as unvoiced or inactive speech.

When all three of the foregoing tests are met (that is,NACF_(sf2)<UNVOICEDTH, bER>0, and vER2>−15) by the signal inputted tothe vocoder, the signal is classified as transient by the vocoder andgiven full rate. Through experimentation it has been determined that,for certain bit rates and carrier frequencies, the DPSK modulationtechnique conditions the carrier signal such that it has thediscontinuities and energy characteristics that cause the vocoder toassign it full rate. The bit rates and carrier frequencies noted abovefor DBPSK have been found to work for the Qualcomm® 4G vocoder. However,different vocoder designs (which often use different speech compressioncodecs) may require the use of a different carrier frequency ordifferent combination of carrier frequency and bit rate to achieve anacceptable bit error rate. For any particular vocoder design, theappropriate frequency and bit rate can be determined by testing thevocoder using sample waveforms. In general, any carrier frequency of4,000 Hz or less (down to about 1 Hz) is preferably used, and morepreferably the carrier frequency is within the range of 400 Hz to 2,500Hz. Apart from the carrier frequency, the bite rate can be selected notjust to achieve a low bit error rate, but also as necessary or desiredfor a particular application. Preferably, the digital data has a bitrate of 250 to 3,000 bits/sec. When selecting a particular carrierfrequency and bit rate, the modulated carrier should be examined at anyof the possible operational modes of the vocoder to insure that the biterror rate is acceptable for the intended application.

Apart from DBPSK, other forms of differential phase shift keyingmodulation can be used as long as they result in a suitable bit errorrate for the particular vocoder involved. For example, FIG. 12 depicts aconstellation plot for differential quadrature phase shift keying(DQPSK) using 5 bits/frame and a 500 Hz carrier. As can be seen fromthis plot, there is a higher bit error rate. Testing of the Qualcomm® 4Gvocoder noted above at the same 500 Hz, 10 bits/frame input that wasused for the DBPSK testing showed a bit error rate of about 6% at allthree operating modes of the vocoder. Although this quadrature approachhas demonstrated a higher bit error rate than DBPSK, it can nonethelessbe used in applications where the higher bit error rate can betolerated. At 1000 bits/sec, DQPSK can be run at frequencies of 900 Hz,950 Hz, and 1350 Hz, again with a 50 Hz variation up or down infrequency to give preferred frequency ranges of 850-1000 Hz and1300-1400 Hz.

Referring back to the BPSK examples of FIGS. 2( b) and 5, and comparingthese modulated signals with the DBPSK example of FIG. 10, it can beseen that the modulated BPSK carriers include discontinuities and energycharacteristics similar to that of the DBPSK modulation of FIG. 10.Thus, the problem with successful transmission of the BPSK modulatedcarrier is not that it cannot achieve transient speech status and obtainfull rate, but that as discussed above, there is a loss of informationbelieved to occur because of phase drifts of the signal. Thus, where itis desired to use PSK (binary or otherwise) and not DPSK, a phasetracker or PLL such as the Costas loop shown in FIG. 13 can be used indemodulating the received carrier signal so that the phase drift doesnot prevent recovery of the encoded data. This Costas loop can beimplemented as a part of the DPSK encoder/decoder 36 used in the modems34, 44 of FIG. 1, and can be implemented in software. The programmingand use of the Costas loop is known to those skilled in the art.

Turning now to FIG. 14, there is shown a second type of DPSK modulationthat can be used to transmit digital data through an EVRC-B vocoder andover a voice channel of the cellular communications system 12. In thisembodiment, DBPSK is used as in the modulation scheme discussed above inconnection with FIGS. 10 and 11, except that it is done by splitting thedigital data into a desired number n of different streams with DBPSKbeing used on each stream to encode a different frequency carrier signalbased on the change between the symbols (i.e., 0 to 1 or 1 to 0) in thedigital data. The modulated carrier signals are then summed together toform a composite modulated carrier signal. When separating the incomingdigital data into the different streams, different portions of the dataare used for each stream so that, for example, where only two streams(two carrier frequencies) are used, alternating groups of the digitaldata (e.g., 10 bytes at a time) are used to modulate carrier signal #1and the remaining alternating groups of digital data are used tomodulate carrier signal #2. The size of each group can be selected asdesired or appropriate for a particular application, whether it be donein larger groups or only as a single bit so that each successive bit ismodulated at a different frequency than its predecessor. The size of thegroups need not be the same so that, for example, larger groups of datacould be encoded at a higher frequency while smaller groups of datacould be encoded at a lower frequency. FIG. 15 depicts an example of twoindividual modulated carrier signals, each at a different frequency, andshows the resulting composite modulated carrier signal after they aresummed together.

Demodulation of the DBPSK data streams can be performed jointly. Thedata streams can be separated out by distinguishing between thedifferent carrier frequencies. Once separated by frequency, the correctdifferential phase can then be determined for each of the known carrierfrequencies, and the digital data can then be recovered through standardDBPSK demodulation techniques.

With an appropriate selection of bit rate and carrier frequencies, theresulting composite carrier signal will have the discontinuities andenergy characteristics necessary to obtain full rate transmission astransient speech through the EVRC-B vocoder. Although this modulationapproach can be used with whatever bit rates and carrier frequencies aredetermined to provide an acceptably low bit error rate, in general, itis preferably used with bit rates from 250-3,000 bits/sec andfrequencies from as low as about 1 Hz up to 4,000 Hz and, morepreferably, from 400 Hz to 2,500 Hz. Highly preferred frequencies foruse with two carrier signal modulation (i.e., n=2) at 1,000 bits/secrate are 650 and 1150 Hz, and 900 and 1400 Hz (or within ±50 Hz ofthese). One frequency pair can be used in one direction over the voicechannel and the other can be used in the other direction.

With reference now to FIG. 16, a further DPSK embodiment is disclosed inwhich frequency shift keying (FSK) is used in conjunction with DPSK(preferably, DBPSK) to encode the digital data. In this embodiment, thedigital data is used to carry out FSK of a carrier signal, switchingbetween two different frequencies in accordance with the digital data.That same data is also used to perform DBPSK of the FSK modulatedcarrier signal. Thus, both frequency and phase of the carrier signal ismodulated and the data is represented both by the particular tone thatis sent (the FSK portion) as well as by the particular phase shift atthe beginning of the tone (the DBPSK portion). Demodulation can beperformed jointly and, once the frequency of a particular symbol isknown, the correct differential phase can then be determined. As aresult of this scheme, the demodulated data will produce 2 bits persymbol of inputted digital data, rather than the 1 bit of the modulationschemes discussed above. Although DBPSK is preferably used, DQPSK andother forms of DPSK can be selected if suitable for a particularapplication. As with the other DPSK modulation techniques discussedabove, the phase shifts in the modulated carrier signal resulting fromthe use of DPSK, along with proper frequency and possibly bit rateselection, give the modulated carrier signal the necessarydiscontinuities and energy characteristics to cause the EVRC-B vocoderto classify the signal as transient speech and assign it full rate. Thegeneral frequency and bit rate ranges specified above for the other DPSKtechniques can be used for this FSK-DPSK modulation scheme. In a morehighly preferred embodiment, at 1000 bits/sec the following frequencypairs can be used (again at frequencies within ±50 Hz of those given):850 and 1400 Hz, 850 and 1450 Hz, 900 and 1350 Hz, 900 and 1550 Hz, 950and 1550 Hz, 1000 and 1550 Hz, 1100 and 1800 Hz, 1150 and 1550 Hz, 1150and 1750 Hz, 1400 and 2050 Hz, 1450 and 2000 Hz, 1500 and 2000 Hz, and1500 and 2050 Hz.

A similar approach to this FSK-DPSK technique is shown in FIG. 17,except that amplitude shift keying (ASK) is used in lieu of FSK. Thegeneral frequency and bit rate ranges specified above for the other DPSKtechniques can be used for this ASK-DPSK modulation scheme. Thus, thebit rate can be from 250-3,000 bits/sec and the frequencies from as lowas about 1 Hz up to 4,000 Hz and, more preferably, from 400 Hz to 2,500Hz. By applying the DPSK modulation to the ASK modulated carrier signal,and by proper selection of bit rate and frequency, the resultingmodulated carrier signal can have the discontinuities (and, thus, lowperiodicity) and energy characteristics necessary to obtain full ratetransmission as transient speech through the vocoder.

As discussed above in connection with FIG. 13, for any of these previousmodulation techniques (e.g., multi-DPSK, FSK-DPSK, and ASK-DPSK),discontinuities in the carrier signal can be achieved using regular PSKrather than DPSK with a Costas loop or other suitable phase tracker usedto avoid the loss of information due to phase drifts.

Referring back momentarily to FIG. 1, it will thus be apparent that, inaccordance with one embodiment of the method of the present invention,digital data can be communicated via the wireless network by:

-   -   (a) modulating one or more carrier signals with digital data        using differential phase shift keying modulation of the one or        more carrier signals, thereby producing a modulated carrier        signal;    -   (b) transmitting the modulated carrier signal across a voice        channel of a wireless telecommunications network;    -   (c) receiving the modulated carrier signal transmitted via the        wireless telecommunications network; and    -   (d) demodulating the received modulated carrier signal back into        the digital data.

In an example where data is being transmitted from the vehicle 20 to thecall center 40, step (a) can be carried out by the modem 34 usingdigital data received from one of the vehicle system modules 38. Step(b) in this example can be accomplished by first using the CDMA 4GVchipset 24 to encode the modulated carrier signal from the modem 34, andthis can be done using a linear predictive codec of the type thatexhibits a time-varying, non-liner transfer function that at leastpartially filters out non-speech components of the inputted data. Theencoded output can then be transmitted over the cellular network 12 viathe vehicle antenna 26. Step (c) of this example then involves receivingthe modulated carrier signal at the call center 40 after it has beenthrough a voice decoder within the CDMA 4GV module 18. Finally, step (d)involves decoding the modulated carrier signal back into the originaldigital data from the VSM 38. Any of the DPSK modulation schemesdiscussed above in connection with FIGS. 11-12 and 14-17 can be used bythe DPSK encoder/decoder 36; alternatively, regular PSK using a Costasloop or other phase tracking at the demodulator can be used.

It is to be understood that the foregoing description is of one or morepreferred exemplary embodiments of the invention. The invention is notlimited to the particular embodiment(s) disclosed herein, but rather isdefined solely by the claims below. Furthermore, the statementscontained in the foregoing description relate to particular embodimentsand are not to be construed as limitations on the scope of the inventionor on the definition of terms used in the claims, except where a term orphrase is expressly defined above. Various other embodiments and variouschanges and modifications to the disclosed embodiment(s) will becomeapparent to those skilled in the art. All such other embodiments,changes, and modifications are intended to come within the scope of theappended claims.

As used in this specification and claims, the terms “for example” and“such as,” and the verbs “comprising,” “having,” “including,” and theirother verb forms, when used in conjunction with a listing of one or morecomponents or other items, are each to be construed as open-ended,meaning that that the listing is not to be considered as excludingother, additional components or items. Other terms are to be construedusing their broadest reasonable meaning unless they are used in acontext that requires a different interpretation.

1. A method of communicating digital data via a wirelesstelecommunications network, comprising the steps of: modulating one ormore carrier signals with digital data using differential phase shiftkeying modulation of the one or more carrier signals, thereby producinga modulated carrier signal; transmitting the modulated carrier signalbetween a call center and a telematics unit, wherein the transmittingstep is carried out by sending the modulated carrier signal via avocoder across a voice channel of a wireless telecommunications network;receiving the modulated carrier signal transmitted via the wirelesstelecommunications network; and demodulating the received modulatedcarrier signal back into the digital data; wherein the modulating stepfurther comprises generating the modulated carrier signal as a compositemodulated carrier signal by carrying out the steps of: modulating afirst carrier signal having a first frequency with a portion of thedigital data using differential binary phase shift keying modulation;modulating a second carrier signal having a second frequency with theremainder of the digital data using differential binary phase shiftkeying modulation; and combining the two modulated carrier signals intoa composite modulated carrier signal.
 2. A method of communicatingdigital data via a wireless telecommunications network, comprising thesteps of: modulating one or more carrier signals with digital data usingdifferential phase shift keying modulation of the one or more carriersignals, thereby producing a modulated carrier signal; transmitting themodulated carrier signal between a call center and a telematics unit,wherein the transmitting step is carried out by sending the modulatedcarrier signal via a vocoder across a voice channel of a wirelesstelecommunications network; receiving the modulated carrier signaltransmitted via the wireless telecommunications network; anddemodulating the received modulated carrier signal back into the digitaldata; wherein the modulating step comprises modulating a carrier signalusing both frequency shift keying modulation and differential phaseshift keying modulation; and wherein the modulating step furthercomprises generating the modulated carrier signal by the steps of: (a)generating an FSK modulated carrier signal by modulating the carriersignal with a portion of the digital data using frequency shift keyingmodulation; and (b) modulating the FSK modulated carrier signal with theremainder of the digital data using differential phase shift keyingmodulation.
 3. The method of claim 2, wherein the differential phaseshift keying modulation comprises differential binary phase shift keyingmodulation.
 4. A method of communicating digital data via a wirelesstelecommunications network, comprising the steps of: modulating one ormore carrier signals with digital data using differential phase shiftkeying modulation of the one or more carrier signals, thereby producinga modulated carrier signal; transmitting the modulated carrier signalbetween a call center and a telematics unit, wherein the transmittingstep is carried out by sending the modulated carrier signal via avocoder across a voice channel of a wireless telecommunications network;receiving the modulated carrier signal transmitted via the wirelesstelecommunications network; and demodulating the received modulatedcarrier signal back into the digital data; wherein the modulating stepcomprises modulating a carrier signal using both amplitude shift keyingmodulation and differential phase shift keying modulation.
 5. The methodof claim 4, wherein the modulating step further comprises generating themodulated carrier signal by the steps of: (a) generating an ASKmodulated carrier signal by modulating the carrier signal with a portionof the digital data using amplitude shift keying modulation; and (b)modulating the ASK modulated carrier signal with the remainder of thedigital data using differential phase shift keying modulation.
 6. Amethod of communicating digital data via a wireless telecommunicationsnetwork using a voice encoder that operates in different modes accordingto a classification of incoming data into categories that include atleast voiced, unvoiced, and transient speech, wherein each of thedifferent modes is associated with a coding scheme for encoding theincoming data, the method comprising the steps of: inputting into thevoice encoder a modulated carrier signal having discontinuities andenergy characteristics that cause the voice encoder to classify themodulated carrier signal as transient speech; obtaining an encodedoutput that is generated by the voice encoder using the inputtedmodulated carrier signal; transmitting the encoded output across a voicechannel of the wireless telecommunications network; receiving theencoded output transmitted via the wireless telecommunications network;generating a decoded modulated carrier signal by decoding the receivedencoded output using a voice decoder; and demodulating the decodedmodulated carrier signal; wherein the method further comprises, prior tothe inputting step, the step of generating the modulated carrier signalby modulating one or more carrier signals with digital data usingdifferential phase shift keying modulation of the one or more carriersignals; wherein the generating step further comprises generating themodulated carrier signal as a composite modulated carrier signal bycarrying out the steps of: modulating a first carrier signal having afirst frequency with a portion of the digital data using differentialbinary phase shift keying modulation; modulating a second carrier signalhaving a second frequency with the remainder of the digital data usingdifferential binary phase shift keying modulation; and combining the twomodulated carrier signals into a composite modulated carrier signal. 7.The method of claim 6, wherein the steps of modulating the first andsecond carrier signals further comprise separating the digital data intoalternating first and second groups of data, modulating the firstcarrier signal with the first group of data, and modulating the secondcarrier signal with the second group of data.
 8. A method ofcommunicating digital data via a wireless telecommunications networkusing a voice encoder that operates in different modes according to aclassification of incoming data into categories that include at leastvoiced, unvoiced, and transient speech, wherein each of the differentmodes is associated with a coding scheme for encoding the incoming data,the method comprising the steps of: inputting into the voice encoder amodulated carrier signal having discontinuities and energycharacteristics that cause the voice encoder to classify the modulatedcarrier signal as transient speech; obtaining an encoded output that isgenerated by the voice encoder using the inputted modulated carriersignal; transmitting the encoded output across a voice channel of thewireless telecommunications network; receiving the encoded outputtransmitted via the wireless telecommunications network; generating adecoded modulated carrier signal by decoding the received encoded outputusing a voice decoder; and demodulating the decoded modulated carriersignal; wherein the method further comprises, prior to the inputtingstep, the step of generating the modulated carrier signal by modulatinga carrier signal using both frequency shift keying modulation anddifferential phase shift keying modulation.
 9. A method of communicatingdigital data via a wireless telecommunications network using a voiceencoder that operates in different modes according to a classificationof incoming data into categories that include at least voiced, unvoiced,and transient speech, wherein each of the different modes is associatedwith a coding scheme for encoding the incoming data, the methodcomprising the steps of: inputting into the voice encoder a modulatedcarrier signal having discontinuities and energy characteristics thatcause the voice encoder to classify the modulated carrier signal astransient speech; obtaining an encoded output that is generated by thevoice encoder using the inputted modulated carrier signal; transmittingthe encoded output across a voice channel of the wirelesstelecommunications network; receiving the encoded output transmitted viathe wireless telecommunications network; generating a decoded modulatedcarrier signal by decoding the received encoded output using a voicedecoder; and demodulating the decoded modulated carrier signal; whereinthe method further comprises, prior to the inputting step, the step ofgenerating the modulated carrier signal by modulating a carrier signalusing both amplitude shift keying modulation and differential phaseshift keying modulation.
 10. A method of wirelessly transmitting digitaldata using an EVRC-B vocoder, the method comprising the steps of:encoding digital data by modulating at least one carrier signal with thedigital data and producing therefrom a modulated carrier signal havingdiscontinuities and energy characteristics that cause the vocoder toclassify the modulated carrier signal as transient speech; inputting themodulated carrier signal into an EVRC-B vocoder; obtaining an encodedoutput from the vocoder; and transmitting the encoded output via anantenna; wherein the encoding step further comprises generating themodulated carrier signal as a composite modulated carrier signal bycarrying out the steps of: modulating a first carrier signal having afirst frequency with a portion of the digital data using differentialbinary phase shift keying modulation; modulating a second carrier signalhaving a second frequency with the remainder of the digital data usingdifferential binary phase shift keying modulation; and combining the twomodulated carrier signals into a composite modulated carrier signal. 11.A method of wirelessly transmitting digital data using an EVRC-Bvocoder, the method comprising the steps of: encoding digital data bymodulating at least one carrier signal with the digital data andproducing therefrom a modulated carrier signal having discontinuitiesand energy characteristics that cause the vocoder to classify themodulated carrier signal as transient speech; inputting the modulatedcarrier signal into an EVRC-B vocoder; obtaining an encoded output fromthe vocoder; and transmitting the encoded output via an antenna; whereinthe encoding step comprises modulating a carrier signal using bothfrequency shift keying modulation and differential phase shift keyingmodulation.
 12. The method of claim 11, wherein the modulating stepfurther comprises generating the modulated carrier signal by the stepsof: (a) generating an FSK modulated carrier signal by modulating thecarrier signal with a portion of the digital data using frequency shiftkeying modulation; and (b) modulating the FSK modulated carrier signalwith the remainder of the digital data using differential phase shiftkeying modulation.
 13. A method of communicating digital data via awireless telecommunications network using a vocoder that encodes andtransmits an incoming data signal at one or more of a plurality ofdifferent rates including a full rate and one or more lesser rates,wherein the rate used by the vocoder to encode and transmit the incomingdata signal is dependent at least in part upon the periodicity of theincoming data signal and characteristics of the energy contained in theincoming data signal, wherein the method comprises the steps of:modulating one or more carrier signals using digital data such that aresulting modulated carrier signal is produced having the followingcharacteristics: a) NACF_(sf2)<UNVOICEDTH; b) bER >0; and c) vER2>−15;where: NACF_(sf2) is a second subframe normalized autocorrelationfunction and UNVOICEDTH is a threshold value based on a determinedsignal to noise ratio; bER is a frequency band energy ratio determinedaccording to the equation ${{bER} = {\log_{2}\frac{EL}{EH}}},$  with ELbeing the amount of energy contained in a lower frequency band of 0-2kHz, and EH being the amount of energy contained in a higher frequencyband of 2-4 kHz; and vER2 is determined according to the equation${{{vER}\; 2} = {{MIN}\left( {20,{10*\log_{10}\frac{E}{vEav}}} \right)}},$ with E being the energy of a current frame of the modulated carriersignal and vEav being the average energy over three previous voicedframes of the modulated carrier signal; transmitting the modulatedcarrier signal across a voice channel of a wireless telecommunicationsnetwork; receiving the modulated carrier signal transmitted via thewireless telecommunications network; and demodulating the receivedmodulated carrier signal back into the digital data.